Green and Silver Concrete Hospital

Dedicated in September 2003, the $53 million Boulder Community Foothills Hospital in Boulder, Colorado, became the first hospital in the nation to receive LEED® certification from the United States Green Building Council. The hospital was awarded a Silver Rating. Designed by OZ Architecture and Boulder Associates, with environmental consulting by Boulder-based Architectural Energy Corporation, the 200,000- square-foot, 60-bed facility features many environmental innovations, including a super-efficient power plant, roofing material that reflects solar heat gain to reduce air-conditioning costs, high-performance windows, and even waterless urinals.

The hospital was carefully placed in the landscape to conserve a wildlife corridor near Boulder Creek. The project location in East Boulder is convenient to bus lines and bike paths that provide alternatives to auto congestion. Extensively landscaped grounds use low-water plantings that create wildlife habitat.

The structural system used in this project was carefully considered for functionality as well as environmental impact. Boulder height restrictions, coupled with the site topography, equated to a building height limit of 46 feet measured from the first floor to the top of the parapet. Based on this height limit, the building was designed with a floor to floor height of 14 feet. Two floor options were evaluated: a cast-in-place conventionally reinforced concrete system and a composite concrete decksteel beam system. With the floor to floor dimension fixed, and allowing for a 10 foot clear ceiling height, the structural depth of the composite floor system allowed for an approximately 18-inch plenum space. Because of the thinner structural depth, the 10.5-inch flatslab concrete option yielded an enormous 38 inches of plenum space. Looking to house substantial mechanical, electrical and plumbing systems in the plenum space, the project team quickly settled on the cast-in-place concrete option for the hospital building frame and floor systems.

Spanning typical building bays of 28-by-28-feet 18-inch square concrete columns support the 10.5-inch thick flat slab. Square drop panels ranging in size from 30- to 36-inches added four more inches enhancing the slab shear capacity at the columns. Floor deflection and vibration is a major concern with steel floor systems, especially under sensitive medical equipment. The concrete floor mass and monolithic construction addressed the design teams concern with deflection and vibration.

“There was a requirement to coordinate rebar locations with the magnetic resonance imaging (MRI) equipment” says David Schafer, Project Architect with OZ Architecture.

Stair and elevator shafts are cast-in-place concrete and provide 100 percent of the lateral force resistance and building stability. Higher strength concrete provides the added stiffness to control building drift without additional shear walls. Flexibility in selecting concrete strengths was put to full use with 3,000-psi foundations, 4,000-psi columns, 5,000-psi floor slabs, and 6,000-psi concrete core and shear walls.

Optimizing the concrete mix design for long term durability, the project team incorporated fly ash to enhance field performance and facilitate obtaining LEED points for recycled content. Fly ash dosage varied from 0 to 25 percent of cementitious materials in order to keep the construction crews and schedules on track. Harvested and manufactured locally, concrete is a good environmental choice, eliminating the environmental impacts of transporting it from other regions. With concrete contributions to LEED silver rating, the project obtained a total of 33 LEED points, including five points for a 35 percent improvement in energy performance over ASHRAE 90 - energy standard for buildings except low-rise residential.

To develop the image as an integral part of the community, the hospital took its exterior design cues from nearby masonry buildings, and the abundant sandstone found in the region. Selected for their warmth and to complement the natural setting, the materials relate well to nearby buildings. Brick and stone were logical environmental choices as well, because they are locally harvested and manufactured with a long lifespan, and minimal maintenance requirements.

Concrete helped the design team achieve their goal of looking at the big picture of healthy communities. With unparalleled durability and energy characteristics, this LEED silver building will save energy and resources, reduce indoor air pollution, increase employee productivity, increase patient comfort, and save money in the long run.